The polysaccharides are a group of carbohydrates composed of long chains of simple sugars, such as for example, starch, cellulose, dextrins, polygalactomannans, chitin, chitosan, alginates, xanthan gum, carageenan gum, gum karaya, gum Arabic, pectin and glass-like polysaccharides as well as other derivatives thereof such as ionic and/or non-ionic derivatives. Examples of starches are: corn, wheat, rice, potato, tapioca, waxy maize, sorghum, waxy sorghum, sago and modified starches such as dextrinated, hydrolysed, oxidized, crosslinked, alkylated, hydroxyalkylated, acetylated, fractionated (e.g. amylose and amylopectin), and physically modified starches.
Polysaccharides have been exploited as absorbent or superabsobents with respect to the uptake of aqueous substances (e.g. water, etc.).
Superabsorbent polysaccharide-based polymers may be obtained through grafting of an unsaturated monomer (acrylonitrile, acrylic acid, acrylamide) onto starch or, less frequently, cellulose. These polymers also called “Super Slurper” showed water absorption from 700 to 5,300 g/g for deionised water and up to 140 g/g in saline solution (Riccardo PO, Water-Absorbent Polymers: A Patent Survey. J. Macromol. Sci., Rev. Macromol. Chem. Phys., 1994, 607-662 (p.634) and cited references). Despite their very high water absorption, these grafted polysaccharides, prepared by radical polymerization are not known to be biodegradable.
Carboxymethylcellulose (CMC) having the following formula
                R=H, carboxymenthyl        m is an integer of from 100 to 12,000is a known polysaccharide-based superabsorbent which is commercially available from numerous vendors (Modern Superabsorbent Polymer Technology, Buchholz F. L. and Graham A. T. ed., Wiley-VCH, Toronto, 1998, pages-239-241 and cited references).        
Carboxymethylstarch (CMS) having the following formula
                R═H carboxymethyl        m is an integer of from 1000 to 3 million for (natural) starchesis another known polysaccharide-based superabsorbent which is also commercially available from numerous vendors are among known polysaccharide-based superabsorbents (Gross and Greuel, U.S. Pat. No. 5,079,354, Jan. 7, 1992, 536/111).        
Anbergen and Oppermann have studied the elasticity and the swelling behaviour of sodium carboxymethylcellulose and hydroxyethylcellulose, chemically crosslinked with divinylsulfone (Andergen U. and Oppermann W., Elasticity and swelling behaviour of chemically crosslinked cellulose ethers in aqueous systems. Polymer, 1990, 31, 1854-1858).
Kabra and Gehrke (WO 95/31500, Nov. 23, 1995, C08J. 9/28) have reported the sorption capacity of hydroxypropylcellulose, crosslinked with different concentration of divinylsulfone (from 0.28 to 2.98 weight %). The best results showed a water sorption capacity of 44 g/g with a crosslink of 0.91 weight %. The authors also mention that other hydrophobically modified carbohydrate polymers can be chosen, such as hydroxypropylstarch.
More recently, SCA Hygiene Products AB (Annergren and Lundstrom. WO 00/21581, Apr. 20, 2000, A61L 15/28, 15/60) extended the study with divinylsulfone to low-cost, readily available, renewable starting materials such as carboxymethylcellulose, carboxymethylstarch, and others.
According to the authors, results may be obtained with a mixture of carboxymethylcellulose: hydroxyethylcellulose (3:1) which absorbs close to 95 g of synthetic urine per g of polymer after free swelling for 120 min. In this patent, however, the quantity of divinylsulfone used is not reported. Divinylsulfone has been applied with respect to other polysaccharides containing acidic groups (Thornton et al. WO 00/35504, Jun. 22, 2000, A61L 15/60, 15/28.). It appears that the best result was obtained with carboxymethylcellulose crosslinked with 14 mol % of divinylsulfone. This results in a centrifuge retention capacity (CRC) of 111 g/g with synthetic urine. On page 6 of WO 00/35504 it has been mentioned that the superabsorbent polysaccharides combine high absorption capacity with control of bacterial growth and control of odour, as well as with biodegradability. There is however no evidence that such compounds would be biodegradable.
Starch ethers have been crosslinked with numerous other bifunctional groups such as acrylamido, chloroazomethine, allyloxy-azomethine groups to give absorbent materials (Holst et al., U.S. Pat. No. 4,117,222, Sep. 26, 1978, 536/50).
There is still a continuing need for environmentally safe and economical producible polysaccharide-based absorbents and superabsorbents and in particular polysaccharide-based absorbents and superabsorbents with at least a significant biodegradability.
Accordingly it would be advantageous to be able to make a cross-linked polysaccharide (and in particular a cross-linked starch) by exploiting a cross-linking agent(s) giving rise to a cross-linked product having desirable water absorption properties. It would in particular be advantageous to be able to make a cross-linked polysaccharide (and in particular a cross-linked starch) by exploiting a relatively cheap cross-linking agent(s). It would further be advantageous to be able to to be able to make a cross-linked polysaccharide (and in particular a cross-linked starch) by exploiting a cross-linking agent(s) giving rise to a cross-linked product having desirable biodegradability properties.